A question was posted in group chat last night asking "Can someone tell me how movers can change numbers on their own?" Someone else said it happened to them as well. And the questioner said it wasn't the first time it had happened to her.
The simple answer is, Movers do not change their dancer numbers by themselves.
There is no function, no action, nothing at all in LSL scripts that can modify the contents of a notecard in an object's or an avatar's inventory.
Likely causes to make you THINK they did: